CN111162284A

CN111162284A - Electrode for working material distribution in fuel cells

Info

Publication number: CN111162284A
Application number: CN201911086551.3A
Authority: CN
Inventors: A·艾费特; C·巴尔迪佐内; H·鲍尔; J·哈肯贝格
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-11-08
Filing date: 2019-11-08
Publication date: 2020-05-15
Also published as: DE102018219066A1

Abstract

An electrode (2) for a fuel cell (1), comprising a plate-shaped body (20) made of electrically conductive foam having an open-pored and continuous porosity for at least one working material of the fuel cell (1). The plate-shaped body (20) ideally defines a plane (E). The plate-shaped body (20) has, in the plane (E), the following zones: the regions have different porosities.

Description

Electrode for working material distribution in fuel cells

Technical Field

The invention relates to an electrode for dispensing at least one working material (Betriebsmitel) for a fuel cell, to a method for producing an electrode, and to a fuel cell having a corresponding electrode.

Background

In a fuel cell, a fuel provided in an anode chamber reacts with an oxidant provided in a cathode chamber.

Such fuel cells are known from the prior art, for example from the publication DE 102009001153 a 1. A known fuel cell comprises two gas diffusion layers, two electrode elements and an electrolyte. The electrolyte is arranged between the two gas diffusion layers with one electrode element each located between them. The fuel cell is supplied with an oxidant, typically ambient air, via a supply line, and a gaseous fuel, such as hydrogen, via a fuel line. Electrochemical reaction of fuel with oxidant occurs in the presence of a catalyst in a fuel cell. The electrolyte must be made ion-conductive for this purpose, preferably such that the cations of the fuel diffuse through the electrolyte. Generally, a polymer is used as an electrolyte.

In order to achieve the best energy density for current generation, it is important that the fuel and oxidant are each distributed evenly over the entire face of the electrolyte. In a further embodiment of the prior art, a distribution structure is introduced for coarse distribution into bipolar plates or end plates which delimit the anode or cathode chamber on the side facing away from the electrolyte, respectively. To which a porous gas diffusion layer is attached as an electrode structure. Document DE 102016213057 a1 discloses an example of a fuel cell in which the bipolar plate comprises a complex distribution structure.

Disclosure of Invention

It is an object of the present invention to design a porous gas diffusion layer such that, in a plane E defined by the gas diffusion layer, the provision of working material on the electrolyte is optimized.

For this purpose, the electrode comprises a plate-shaped body made of an electrically conductive porous structure, such as, for example, an electrically conductive foam, which has an open-cell (ofen) and is continuous for at least one operating material of the fuel cell

The porosity of (a). The plate-shaped body ideally defines a plane. The plate-shaped body has the following areas in this plane: the regions have different porosities.

Thus, the plate-shaped body can be equally considered as a gas diffusion layer and an electrode. The porosity of the plate is random and behaves opposite to its density. However, the density can be increased in a targeted manner, for example by pressing. The working material, i.e. preferably hydrogen or air, flows in this plane; the flow is affected by different porosities. The electrolyte is supplied with the working material in a direction perpendicular to this plane. In order to supply the electrolyte of the fuel cell with the reactants or working materials as homogeneously as possible, it is advantageous to provide the irregular structure of the gas diffusion layers or of the electrodes, as will be explained in more detail below.

Advantageously, the plate-shaped body has a first region with a higher porosity and a second region with a lower porosity. Thus, the foam of the second region is denser (dicht) than the foam of the first region. This is achieved, for example, by: the second region is more strongly compressed perpendicular to the plane than the first region. The flow of the working material in this plane can thereby be distributed or guided very well.

In an advantageous embodiment, the porosity in the second region is reduced by deformation. Thus, the first and second regions may first be manufactured from the same foam having the same porosity and then the porosity of the two regions may be adjusted differently by deformation, e.g. extrusion, preferably by using different initial heights before extrusion. Advantageously, the porosity of the second region is reduced by a maximum of 60%.

Preferably, the flow cross-section Q of the first region₁Is the flow cross section Q of the second region₂One fifth to 5 times as large.

In an advantageous embodiment, the first region is formed by a first strip and the second region is formed by a second strip. Preferably, a plurality of first strips and second strips are arranged side by side in the plane in an alternating manner. The main flow direction of the working material in this plane thus extends in the direction of the strip, where the working material preferably flows through the first strip with the higher porosity.

An advantageous method for producing such an electrode provides the following method steps:

alternately arranging the first strips and the second strips side by side, wherein the first strips first have a first height and the second strips first have a second height,

the first and second strips are then pressed to a uniform height, such as by conventional pressing or rolling.

This results in an electrode having a uniform height, which can therefore be arranged in a known manner in a fuel cell between the electrolyte and the end plate. Preferably, the two strips are first made of the same foam with the same random porosity, but of exactly different heights; the different porosities are adjusted by mere squeezing.

A first height piece (Scheibe) was cut from one block of foam. The pieces of the second height are cut from another piece or the same piece. The sheet is cut into strips, i.e. into a first strip and a second strip. Next, the first and second strips are alternately arranged side by side. Alternatively, the strips may be joined by gluing, welding or preferably laser welding for better handling. As a variant, the foams of the two pieces can have different porosities and/or materials and/or the cutting is preferably guided such that sheets of different thicknesses are produced. Particularly preferably, the electrodes made of the combined strips are then pressed to a uniform height h, so that, in particular, regions of different porosity can be formed.

Thin foams, in particular metal foams, are produced here, for example, by cutting large blocks from wire, into thin foam sheets. These foam sheets must have a uniform thickness or height for low tolerance stacking and can therefore be adjusted to the thickness by means of a rolling device with optional heating.

In a further advantageous embodiment, the first region is formed by a substrate and the second region is formed by a post, which is arranged in a hole of the substrate. The struts are preferably circular in planar cross section and are arranged here in such a way that they are aligned on a plurality of parallel lines and thus form the main flow direction. Advantageously, the pillars have a smaller porosity than the substrate, so that the pillars are relatively flow-hindered. However, since the pillars are surrounded over their entire circumference by a substrate with better flow permeability, this is achieved particularly uniformly: the electrolyte is supplied with the working material, i.e. by flow perpendicular to the plane, and thus also at the location of the column. The flow perpendicular to the plane can also be achieved particularly uniformly by the distribution of the flow through the column in the plane of the electrolyte.

In a preferred embodiment, the base plate is of substantially rectangular design and the columns are arranged in alignment with approximately diagonally parallel lines. This results in a diagonal main flow direction, so that the entire surface of the plate-shaped body is supplied with working material very uniformly. This applies in particular when the inlet and outlet openings for the working material into and out of the plate-shaped body are arranged diagonally opposite one another and are ideally constructed in a site-shaped manner.

Accordingly, the invention also includes a fuel cell having an anode compartment, a cathode compartment, and an electrolyte separating the anode compartment from the cathode compartment. The anode and cathode chambers are each bounded on the side facing away from the electrolyte by end plates. An electrode as described above is arranged between on the one hand at least one end plate and on the other hand the electrolyte. This has the effect, inter alia, that the fuel cell as a whole can be constructed very thinly.

In a preferred embodiment, the base plate of the electrode is of substantially rectangular design, and the columns are arranged in alignment with approximately diagonal parallel lines. The fuel cell has an inlet and an outlet for the working material to and from the plate-shaped body. The inlet and outlet are arranged diagonally opposite on the plate-shaped body. The connection between the inlet and the outlet thus corresponds approximately to the main flow direction or is oriented according to parallel lines. The working material is thus supplied to the electrolyte particularly uniformly. The working material not fed to the electrolyte leaves the plate-shaped body via the outlet, but can be recirculated if necessary.

An advantageous method for producing an electrode having a cylindrical second region provides the following method steps:

holes are formed in a substrate, for example by stamping, the substrate having a first height h₁；

Arranging a post in the hole, the post having a second height h₂Wherein h is₂Greater than h₁；

The substrate and posts are then pressed to a uniform height h, for example by conventional pressing or rolling.

The substrate and posts are preferably first made of foam having the same random porosity. After the pressing, the porosity of the pillars is significantly reduced more than the porosity of the substrate, which may even remain unchanged.

Another advantageous method for producing an electrode having a cylindrical second region provides the following method steps:

arranging pillars on a substrate having a first height h₁Said column having a height h₂-h₁Wherein h is₂＞h₁And, due to subsequent processing steps, at least temporarily connecting the posts with the substrate;

Advantageously, the median pore size of the electrode material or of the finished electrode is between 100 μm and 400 μm, at least in partial regions. The lower bound gives rise to: the pressure loss of the working material does not become excessive. The upper bound causes: the distribution of the working material is also fine enough on the surface of the electrolyte.

The invention also relates to another method for manufacturing the electrode from the electrode material. In this method, the foam of the second region, i.e. for example of the second strip or of the column, is at least temporarily compressed by at least 20% and at most 60% in terms of its thickness. That is, the height h is located at the second height h₂In the range of 40% to 80%.

It has been recognized that the porosity in the electrode is changed precisely when compressed in this region to such an extent that the flow of working material is thereby guidable in the electrode, while at the same time the porosity of the openings remains in the entire electrode and no region is completely excluded by the supply of working material. The electrode can fulfill the dual function of a distribution structure and a diffusion layer as working material particularly well as described above.

In this context, it is considered that the foam partially rebounds again after the compressive force is removed. Thus, the deformation is partly plastic and partly elastic.

Advantageously, for extrusion, at 200N/cm²And 3000N/cm²The pressure between loads the foam. The loading is significantly at 150N/cm²Above the typical pressure to which the finished electrode is subjected under compression, typically in a fuel cell or fuel cell stack. The linear pressure in this region leads to an at least partially plastic deformation of the foam without completely closing or destroying the foam too porous.

Drawings

Further measures which improve the invention are shown below in connection with preferred embodiments of the invention in the following description of the figures.

Fig. 1 shows an exemplary embodiment of an electrode, wherein only the main regions are shown;

FIG. 2 shows another exemplary embodiment of an electrode, wherein only the main regions are shown;

FIG. 3 shows another exemplary embodiment of an electrode, wherein only the main regions are shown;

fig. 4 shows a schematic side view of a fuel cell, wherein only the main regions are shown.

Detailed Description

Fig. 1a, 1b and 1c show an embodiment of an electrode 2. Fig. 1a and 1b show the electrode 2 in a side view and fig. 1c in a top view. Fig. 1a shows the electrode 2 before extrusion or before fabrication; fig. 1b and 1c show an electrode 2 after pressing or as a finished electrode 2, which can be arranged, for example, in a fuel cell. The electrode 2 is produced with a length l, a width b and a height h, wherein the following applies: l is more than or equal to b and more than or equal to h. Fig. 1a, 1b and 1c are only schematically shown and should be understood as not to scale.

The electrode 2 consists of a plate-shaped body 20 of length l and width b, which define a plane E. The subject matter of the invention is the gas flow or the flow of the working material in the plane E of the plate-shaped body 20 or the distribution of the working material in the plane E, wherein, obviously, in an application for the fuel cell 1, there must also be a flow of the working material in the direction of the height h for supplying the electrolyte 3, as will also be shown subsequently in fig. 4.

The plate-shaped body 20 is preferably embodied in metal. The plate-shaped body 20 is furthermore embodied as a porous foam, so that a gas flow, for example air or hydrogen, is possible through it. Especially for applications in polymer electrolyte fuel cells, the foam or plate-shaped body 20 must also be able to conduct away the reaction water on the cathode side. Furthermore, the plate-shaped body 20 must be electrically conductive. In order to optimize the gas flow and, if appropriate, the water removal, the electrode 2 according to the invention has regions in the plate-shaped body 20 which have different porosities, i.e. a first region with a higher porosity and a second region with a lower porosity.

For this purpose, the foam is cut to a first height h, for example in block form, with a random regular porosity₁ First strip 21 and a second height h₂Of a second strip 22 of, wherein h₂＞h₁H (see FIG. 1 a). The first strips 21 and the second strips 22 are now arranged alternately side by side and are then pressed or rolled to a uniform height h (see fig. 1 b). The resulting electrode 2 thus has a relatively high porosity (i.e. low density) in the first strip 21 and a relatively small porosity (i.e. high density) in the more strongly pressed second strip 22. The first strip 21 corresponds in this embodiment to a first zone and the second strip 22 corresponds to a second zone.

The gas flow is thus predominantly realized in the first strip 21 during operation of the fuel cell. In the embodiment of fig. 1a, 1b, 1c, the first strips 21 and the second strips 22 have a length corresponding to the width b of the electrodes 2; the first strip 21 and the second strip 22 are thus arranged such that the gas flow is effected in the main flow direction 70 in the plane E mainly in the direction of the width b. Preferably, the flow cross section Q of the region of higher porosity in the main flow direction 70₁Flow cross section Q being a region of lower porosity₂One fifth to 5 times as large.

Fig. 1b shows the actual flow cross section Q in plane E₁And Q₂. Actual flowThe dynamic cross section corresponds to the product of the height h and the width of the first strip 21 or the second strip 22.

The present invention is clearly similar to gas flow achieved primarily in the direction of length l; accordingly, the first strips 21 and the second strips 22 will have a length corresponding to the length l of the electrode 2.

Fig. 2 shows a top view of another embodiment of the electrode 2. The electrode 2 of fig. 3 also consists of a plate-shaped body 20, which is embodied as a foam and preferably as a metal. As in the embodiment of fig. 1, the foam is carried out porous, but now does not have strips of different porosity, but rather ideally has posts 32 of point-like different porosity, or in the embodiment of fig. 2, of lesser porosity.

Fabrication here is achieved similarly to the embodiment of fig. 1 a: the plate-shaped body 20 essentially consists of a base plate 31 of foam. First height h of plate-shaped body 20₁The substrate 31 is partially perforated by punching or laser cutting. The hole 31a thus created is provided with a second height h of greater height₂Wherein the post 32 and the substrate 31 first preferably randomly have the same porosity. Then, the plate-shaped body 20, i.e. the base plate 31 and the studs 32, is pressed to a uniform height h, wherein h is less than or equal to h₁. In this way, regions of low porosity are produced at the insertion point or on the post 32, so that the pressure loss can be locally varied by means of the insertion method. The shape of the "dotted" area is arbitrary, preferably, however, circular. Optionally, the inserted pieces or posts 32 are joined to the base plate 31 by welding or laser welding before or after pressing. Thus, in this embodiment, the substrate 31 constitutes a first region of higher porosity, while the pillars 32 constitute a second region of reduced porosity.

The main flow direction 70 in the plane E of the embodiment according to fig. 2 can be realized either along the width b or along the length l of the electrode 2, depending on how the inlet and outlet openings are arranged on the electrode 2. Flow cross section Q with higher and lower porosity₁And Q₂In this case, the main flow direction 70 is described along the width b and are situated adjacent to one another, such as the diameter of the column 32, with respect to the main flow direction 70The spacing between the pillars of (a) behaves like.

Fig. 3 shows a further electrode 2 with a plate-shaped body 20 having a base plate 31 and a column 32, which originally have different heights h₁And h₂And has been pressed to a uniform height h so that the foam of the plate-shaped body 20 has the following areas: the regions have different porosities; the substrate 31 constitutes a first region and has a relatively high porosity; the pillars 32 constitute the second region and have a relatively low porosity. But alternatively the same height h₁And h₂It is also possible to use substrates 31 and columns 32 of different foams with the same result with different porosities.

In the embodiment of fig. 3, the pillars 32 are arranged diagonally or approximately diagonally, preferably at an angle between 30 ° and 60 °, in the plane E with respect to the length l and the width b of the electrode 2. The columns 32 are thus aligned along parallel lines 71, which accordingly extend diagonally. Accordingly, the main flow direction 70 of the working material also extends correspondingly diagonally, i.e. parallel to the line 71, in particular if the inlet 5 and the outlet 6 of the working material are likewise arranged on diagonally opposite ends of the electrode 2 in the plane E. Accordingly, the flow cross section Q of the region of higher and lower porosity is depicted in plane E perpendicular to the main flow direction 70₁And Q₂。

Fig. 4 shows an embodiment of the fuel cell 1. The fuel cell 1 has an anode chamber 1a and a cathode chamber 1b, which are separated from each other by an electrolyte 3; the electrolyte 3 is preferably embodied as a polymer electrolyte membrane. The anode chamber 1a is delimited in the thickness direction of the fuel cell 1 by a first end plate 11 on the one hand and an electrolyte 3 on the other hand. The cathode chamber 1b is delimited by a second end plate 12 on the one hand and an electrolyte 3 on the other hand. The lateral and circumferential seals are not shown in fig. 4 for the sake of clarity.

In each of the anode chamber 1a and the cathode chamber 1b, an example of such an electrode 2 is provided, which is of the type shown in fig. 1 to 3. In the embodiment of fig. 4, the electrodes 2 are embodied identically in the anode chamber 1a and the cathode chamber 1b, but this is absolutely not absolutely necessary. For example, it is possible to provide the electrode 2 with an average higher porosity in the cathode chamber 1b, so that the product water can be optimally removed.

The electrode 2 according to the invention has the following advantages here:

the possibility of applying open-cell foams with high porosity and large pores in order to achieve low pressure losses;

the targeted introduction and production of regions of higher rigidity, i.e. lower porosity, results in a higher structural strength of the foam.

With overall smaller pressure losses, better lateral exchange of the flow is achieved by the points or strips with higher pressure losses.

A region with layers (autoflage) which are modified in the direction of the electrolyte 3 in order to limit the intrusion of open-cell foam ends into the electrolyte 3 or an intermediate layer arranged therebetween.

Claims

1. An electrode (2) for a fuel cell (1), comprising a plate-shaped body (20) made of electrically conductive foam having an open-pored and continuous porosity for at least one working material of the fuel cell (1), wherein the plate-shaped body (20) ideally defines a plane (E), characterized in that the plate-shaped body (20) has the following regions in the plane (E): the regions have different porosities.

2. The electrode (2) according to claim 1, characterized in that said plate-shaped body (20) has a first region (21, 31) with a higher porosity and a second region (22, 32) with a lower porosity.

3. The electrode (2) according to claim 2, wherein the porosity in the second region (22, 32) is reduced by deformation.

4. Electrode (2) according to claim 2 or 3, characterized in that the flow cross section Q of the first region (21, 31)₁Is the firstFlow cross-section Q of the two regions (22, 32)₂One fifth to 5 times as large.

5. The electrode (2) according to any of claims 2 to 4, characterized in that the first region is formed by a first strip (21) and the second region is formed by a second strip (22), wherein preferably a plurality of first strips (21) and second strips (22) are arranged alternately side by side in the plane (E).

6. The electrode (2) according to any of claims 2 to 4, characterized in that the first region is formed by a substrate (31) and the second region is formed by a post (32) arranged in a hole (31a) of the substrate (31).

7. The electrode (2) according to claim 6, characterized in that the substrate (31) is substantially rectangular in configuration and the pillars (32) are arranged in alignment with approximately diagonal parallel lines (71).

8. A fuel cell (1) having an anode chamber (1a), a cathode chamber (1b) and an electrolyte (3) which separates the anode chamber (1a) from the cathode chamber (1b), wherein the anode chamber (1a) and the cathode chamber (1b) are each bounded on the side facing away from the electrolyte (3) by an end plate (11, 12), wherein an electrode (2) according to one of claims 1 to 7 is arranged between at least one end plate (11, 12) on the one hand and the electrolyte (13) on the other hand.

9. A fuel cell (1) having an anode chamber (1a), a cathode chamber (1b) and an electrolyte (3) which separates the anode chamber (1a) from the cathode chamber (1b), wherein the anode chamber (1a) and the cathode chamber (1b) are each bounded on the side facing away from the electrolyte (3) by an end plate (11, 12), wherein an electrode (2) according to claim 7 is arranged between at least one end plate (11, 12) on the one hand and the electrolyte (13) on the other hand, wherein the fuel cell (1) has an inlet (5) and an outlet (6) for the working material to enter and exit the plate-shaped body (20), wherein the inlet (5) and the outlet (6) are arranged diagonally opposite on the plate-shaped body (20).

10. A method for manufacturing an electrode (2) according to claim 5, wherein the first strips (21) first have a first height (h)₁) And the second strip (22) first has a second height (h)₂) Wherein the first strip (21) and the second strip (22) are arranged side by side and then the first strip (21) and the second strip (22) are pressed to a uniform height (h).

11. A method for manufacturing an electrode (2) according to claim 6 or 7, wherein the substrate (31) first has a first height (h)₁) And, the column (32) first has a second height (h)₂) The method is characterized by comprising the following steps:

-structuring a hole (31a) in the substrate (31), for example by stamping;

-arranging said post (32) in said hole (31 a);

the substrate (31) and the posts (32) are then pressed to a uniform height (h), for example by conventional pressing or rolling.

12. A method for manufacturing an electrode (2) according to claim 6 or 7, wherein the substrate (31) first has a first height (h)₁) And, the column (32) first has a second height (h)₂) Characterized by the following method steps,

arranging pillars (32) on the substrate (31) and connecting the pillars at least temporarily with the substrate (32) as a result of a subsequent processing step;

13. A method for manufacturing an electrode (2) according to any of claims 10 to 12, wherein the foam of the second region is compressed in its height by at least 20% and at most 60% when pressed.

14. The method of claim 13, wherein, for extrusion, the pressure is at 200N/cm²And 3000N/cm²The pressure between loads the foam.